1. Field of the Invention
The present invention relates generally to the field of resonance compensation, and more specifically to compensating for hard disk drive head suspension mechanical resonance effects, such as torsion and sway.
2. Description of the Related Art
Disk drives are magnetic recording devices used for the storage of digital information. Digital information is recorded on substantially-concentric tracks on either surface of one or more magnetic recording disks. Disks are rotatably mounted on a spindle motor, and read/write heads mounted to actuator arms access information on the disks, with the heads rotated by a voice coil motor (VCM). The voice coil motor rotates the pivoting arms, or suspensions, and moves the heads radially over the surface of the disk or disks. The read/write heads must generally be accurately positioned on the disk to ensure proper reading and writing of information that will define the data storage tracks. After the system writes the servo patterns on the disks, each disk can be added to a hard drive assembly.
The information contained in servo and data tracks on the disk surface must be written in a precise manner. In a typical configuration, one or more data heads are employed and are connected to a rotatable base via a suspension, or arm, that has particular mechanical characteristics. The resonance behavior of the arm is highly determinative of the accuracy of data written and read by the head, as significant resonance in the arm or suspension can significantly disturb head position.
Testing of disk drive suspension mechanical resonance characteristics requires devices such as a Head Resonance Tester, or HRT, to excite various resonance modes on the combined suspension and head assembly by shaking the assembly. The HRT, or shaker, may excite resonance modes within certain ranges, including but not limited to 1 KHz to 40 KHz. If the head is mounted onto the suspension and centered along a suspension axis, the HRT may shake the suspension and head arrangement in a line perpendicular to the suspension axis, which may be called the Z axis. In essence, the base of the suspension is fixed and shaken in a direction perpendicular thereto, such as the arrangement shown in FIG. 6. Loaded HRT 601 includes accelerometer 401, shaker block 402, suspension 404, and head 403. The amplitude of the HRT excitation in the arrangement shown may be measured by the accelerometer 401.
For the arrangement shown in FIG. 5, when the direction of acceleration does not remain well aligned in the Z direction, the accuracy of the resonance curve generated by the accelerometer may be compromised. Such misalignment can result from resonance modes in the HRT, which can be very difficult to prevent over large frequency ranges. Further, the interaction between the suspension and the HRT, specifically the action of the suspension resonance on the shaker block, can also cause the suspension to torque and move in directions other than the Z direction in the arrangement shown. The additional movement is not measured by the accelerometer but is a component describing the rotational motion of the shaker block 402. These spurious motions, sometimes referred to as shaker modes, provide an additional non-characterized excitation to the suspension and head and thereby limit the accuracy and usefulness of resonance measurements.
It would be beneficial to have a system that overcomes the shortcomings of previous designs and provides a more accurate assessment and correction of resonance curves for a mechanical arrangement, such as a drive head and suspension combination.